Many insects provide humans with unheralded services such as pollination, sustenance, and pest control, but some of them gross us out — or worse. Take dung beetles such as the one shown in this image, for example. As their name implies, the insects process feces for their livelihoods. The service helps reduce fertilizer costs on grazed agricultural lands and cuts down on the number of flies and parasites the piles of manure would otherwise attract. But a life of dung? Ick.

Click the "Next" arrow above to learn about seven more insects with "ick" factors that make us squirm, or much worse.

— By John Roach, msnbc.com contributor

Head lice, the annoying itch

Sean Gallup
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Getty Images file

For moms and dads, the thought of head lice can sow panic at home. School-age kids are prone to pick up the feared infestation of the sesame-seed sized insects in packed classrooms. The critters latch onto hair follicles and feed on tiny drops of blood. At first sight of head lice, many school nurses send infected — and itchy — students straight home. And that's when parents freak out, lathering their kids with shampoos, gels and creams in an effort to kill the lice. However, some lice are proving resistant to the treatments, leaving parents scratching their heads over what to do.

Adults, perhaps in the kid-making stage, are also panicked by another kind of lice: crabs. These critters nest in pubic hair and are often transmitted in the course of sexual intercourse. Crab-inspired panic attacks, however, might be on the way out. Researchers at the University of Leeds in Britain noted a decline in crab infestations, first among women and then men, reported at their clinic. The researchers speculated in the journal of Sexually Transmitted Infections that the decline is due to the popularity of the so-called Brazilian bikini wax, which removes most pubic hair, The Associated Press reported.

It's getting harder to stop the bedbugs from biting

Scherzinger Pest Control

The adage about bedbugs is getting harder to follow, according to entomologists and pest control experts who have noted an uptick in infestations of the blood-sucking insects. Heavy use of insecticides such as DDT all but eradicated bedbugs from the U.S. by the late 1960s, but international travelers appear to have re-opened the door and now, media reports suggest, bedbugs are back with a vengeance. The insects attack warm bodies in the middle of the night and then retreat to dark crevices behind headboards and mattresses. Telltale signs of their presence include pepperlike fecal spots and shed skins.

Cockroaches have few fans

Science

Garbage-loving, foul-smelling and house-infesting cockroaches have few admirers beyond Disney-Pixar's animated robot Wall-E, whose only friend on a post-apocalyptic Earth is, naturally, among the world's most enduring insects. The notoriously difficult-to-kill bugs can spread disease and cause allergies. Researchers are hoping baits that mimic the pheromones females give off when they are ready to mate can at least give humans an edge in the battle for pest-free environments. In this image, a female cockroach at upper right attracts three males with her scent.

Ticks, although not technically insects (they're arachnids like spiders and mites), make some people bug out. The critters crawl onto hosts such as dogs and people and burrow in their heads to suck blood. Ticks can go undetected for days, ample time to spread sometimes fatal illnesses such as Lyme disease and Rocky Mountain spotted fever. Prevention requires application of insect repellant when outside and regular body checks for potential bites. If a tick is detected, experts advise not to panic, but to expeditiously remove the tick by grasping it with tweezers as close to the skin as possible and pulling upward with steady, even pressure. A brown dog tick is shown here.

Fleas no fun for Fido or his best friend

DesignPics Inc. via Newscom file

The "how cute" reaction evoked by scenes such as the one shown here can quickly change to "ick" when our dogs start gnawing on their fur to rid themselves of fleas. The wingless, blood-sucking insects can also be more than an itchy nuisance: they are known to spread bubonic plague between rodents and humans, which has killed millions of people. Experts recommend frequent vacuuming, regular washing of pet bedding and treating household pets with topical insecticides.

Mosquitoes the icky and deadly

Rothamsted Research

For many of us, mosquitoes are more annoying than nasty; though most of us have uttered an ick or two when we successfully swat one on an exposed arm or leg only to create a skid mark of our own blood and bug. But more than ick, the insects are vectors of lethal disease. More than a million people each year die from malaria, a disease caused by parasites in red blood cells that is spread by mosquitoes in some parts of the world such as Africa. In an experiment with a twist, scientists attempting to develop a malaria vaccine recently successfully used mosquitoes to vaccinate humans against the disease.